The invention relates to a Fourier transform infrared spectrophotometer (hereinafter referred to as “FTIR”) provided with an optical element made of a material with deliquescence property, more specifically, relates to a method for removing moisture in a chamber storing the optical element.
An optical material with deliquescence property (a property of absorbing and dissolving moisture in air) such as KBr has been used for an optical element such as a beam splitter or the like in an interferometer of FTIR. Therefore, in order to prevent the deliquescence of the optical material, the interferometer including such an optical element as described above is stored in a sealed chamber with a drying agent such as a silica gel for removing moisture therein.
Incidentally, in general, as the moisture is absorbed, an ability of the drying agent to absorb the moisture is lowered. Therefore, it is necessary to exchange the drying agent periodically to maintain the ability of absorbing moisture at a desired level.
In the FTIR described above, air enters the sealed chamber when the drying agent is exchanged. Accordingly, it is difficult to exchange the drying agent in a high humid environment. For this reason, when the drying agent is exchanged, it is necessary to move the FTIR to a place with a low humidity.
It is troublesome to exchange the drying agent periodically. However, if the drying agent is not exchanged for a long time while the FTIR is used frequently, it is possible to damage the optical element due to the deliquesce.
In order to reduce a frequent exchange of the drying agent in the FTIR using an optical material with deliquescence property, Japanese Patent Publication (KOKAI) No. 10-253454 has disclosed an FTIR having a sealed chamber in which an interferometer using an optical material with deliquescence property and a heater for an infrared light source are arranged. A box member including a drying agent is disposed adjacent to the heater for the infrared light source. The box member further includes a first opening for communicating with an atmospheric air side, a second opening communicating with the sealed chamber side, and a valve for opening one of the two openings. In the FTIR, the heater for the infrared light source dries and regenerates the drying agent while the FTIR is in use. The valve of the box member opens the first opening to the atmospheric air side when the FTIR is in use, and the second opening to the sealed chamber side is opened while the FTIR is not in use.
The present invention has been made to solve the problems mentioned above with a method different from that disclosed in Japanese Patent Publication No. 10-253454, and an object of the invention is to provide an FTIR wherein it is not necessary to exchange the drying agent at all, or frequently.
Further objects and advantages of the invention will be apparent from the following description of the invention.